Humans rely on multiple types of sensory information to localize targets for reaching, with vision and proprioception most heavily used. However, situations arise where one modality might be more useful than the other (e.g. vision is poor in a dark room). Presumably, the usefulness of different modalities constantly changes, making it advantageous for the nervous system to be able to dynamically switch which modality it "listens to" the most. We call this process sensory re-weighting. Additionally, in most situations it is optimal to combine information from different modalities to estimate a target location. It is therefore critical that they be aligned with one another. Situations can arise when vision and proprioception become misaligned (e.g. wearing glasses with prisms). When sensory modalities become misaligned, it is advantageous for the nervous system to bring the two back into register. We call this process sensory re-alignment. Re-weighting and re-alignment may be two separate processes that are optimally used alone in some situations and in combination in others, and therefore functionally and neurologically distinct. Here we propose to study these behavioral processes in humans. Using psychophysical techniques, we will determine whether the two are separable, and we will ascertain the rules by which the nervous system governs them. We will also determine whether overlapping or distinct brain circuits are important for these processes by studying individuals with focal brain damage, initially focusing on the cerebellum and parietal lobe. Finally, we will discuss how these processes might be manipulated to compensate for deficits in patient populations. The brain's ability to optimally combine different kinds of sensory information is critically important for precise movement control in different contexts (e.g. poorly lit rooms). The ability to align different kinds of sensory information is also critical for behavior, allowing people to benefit from multiple sources of information about the location of objects in their environment. People who lose either of these abilities lose behavioral flexibility and movement accuracy;a better understanding of the rules of sensory integration and adaptation should allow us to understand how to train individuals to improve these abilities, and ultimately movement control.